I've finally decided on my perks that 'work', I'll walk you through a brief history of what I used to use.
 
When I  first got the game, herp derped around using everything, sucked, averaged about 0.33 KD.
 
Got used to the Galil and stuck with it, used Scavenger (first thing I got to pro) alongside Warlord (also got to pro relatively fast). Stuck with Second Chance because I found it hilarious to shuffle towards the enemy. KD finally started to hit 'balance', a clean 1.
 
Discovered Hardline before it was patched out, got pro stupidly fast and changed all my killstreaks to airdrops. Ended up every match using around 2 choppers/dogs/bombing runs etc etc, laughed my ass off as KD rose to stupid levels.
 
Hardline got patched, suddenly I sucked again, I was prestige 1 by this point so I should have known better...here is where I started to play Nuketown 24/7 servers and my loadout changed, this is also when the game 'worked' for me and allowed me to get games with 5+ K/D ratio and some slick play.
 
I was a big fan of Hacker as I hated dying to claymores, what was annoying me even more however was Nova Gas...deaths via claymores on Nuketown wasnt much of a worry, so many explosions and grenades they always get destroyed anyway. So I took the Mask and changed my tacticals to Gas, instantly I could storm into rooms and literally clean house most of the time, there seems to be a huge wave of Ninja Pro users currently so few others are resistant to it.
 
This got me thinking, Hardline was meh for me now, Scavenger never quite popped with me, Lightweight really only strikes me as something for the knife players and I cant use Ghost because I'm useless at stealth and hiding effectively... so Flak Jacket then? So far I'm immune to Nova Gas and resistant to explosives, skip forward a few games, I'm throwing back frags without fear, standing in napalm strikes and gas grenades laughing, simply walking towards flashbangs and shrugging them off in a second or two...it felt almost overpowered, for my playstyle atleast.
 
Long story short anyway, I have finally found 'my' setup, prestige 1 level 34....and I finally figured it out. Flak pro, Sleight Pro, Mask Pro. I will play this until prestige 15 and I will smile all the way, safe in the knowledge I will never again kill myself...and only myself...with a napalm strike.
 
So how about the community? Anyone finally find their 'build' and simply found a whole new side of joy to the game?

What the fuck happened to the perk system since CoD4? Resistant to explosives "nova gas" and flashbangs? I dont even know what half those things are.

I really haven't tweaked my style much, found what worked for me and stuck with it. Ghost Pro, Warlord Pro, Last Stand Pro. The Gail w/ a silencer and I always use claymores, usually finish with 2+ k/d. I have tried other setups, more run and gun style, but I just die constantly. What can I say, I am a camper. Not that I just stick to one corner or spot, I move around the map and always have my back to a wall. I like to win so I play slow and careful.

I've been Flak Pro,  Sleight Pro and Hacker Pro predominantly.
 
I think when I prestige I'm gonna try running Flak, Warlord and Tac Mask together.  Love Flak to death, Warlord offers Dual Mags for a Scavenger/Sleight mini replacement and an optical attachment (as well as more grenades), and then Tac Mask so I don't blind/stun myself. 
 
Will it work as I plan?  Probably not.  But that's what has been rolling around in my head.  :)

I use Ghost pro, Sleight of Hand pro, and Hacker pro.

The quest to find your perfect perk set up is one of the things I like most about the COD multiplayer. 
 
I did have ghost pro, sleight pro and ninja pro with a silencer on my gun but i'm feeling a change coming on. 
 
Flak Jacket seems cool and I might try the gimp mask out as well XD

The closest I got was unlocking Sleight of Hand Pro. That at least stopped the situations where someone killed me solely because he had the faster ADS and I didn't, but I still had maybe one good match in 20. Quit a while ago.